Typical dozing machines comprise a tractor having a dozer blade carried at the front end thereof. In many instances, the tractor is a track-driven machine having a pair of mutually-spaced tracks that are driven to propel the machine. As such, ordinary steering of the machine is accomplished by varying the relative speed of the tracks. In simple cases, a conventional clutch and brake arrangement is provided to selectively cut power to one of the tracks to cause the machine to steer. In other machines, however, socalled differential steering is possible in which the speed of one track is increased while the speed of the opposite track is decreased.
One problem with the clutch and disc steering arises when the machine is operated with a substantial blade load. When power to one track is cut, the remaining driven track may not have sufficient tractive force to maintain the forward motion of the machine. This may be a particular concern when the machine is operated in a "cruise control" mode to maintain a desired forward speed. Thus, it is desirable during steering to maintain power to both tracks when operating under substantial blade loads to thereby maintain the forward speed of the machine. Differential steering may be used to address this problem but can be complex and adds to the cost of the machine.
One known solution to the aforementioned problem which does not require differential steering is the use of blade tilt steering. More particularly, steering can be accomplished by tilting the dozer blade about the longitudinal axis of the tractor to raise or lower one side of the blade during a push. Such blade tilting during a pushing operation causes the blade to dig deeper at one side, which creates a positive yaw rate. An example of blade tilt steering is described in U.S. Pat. No. 5,487,428, issued on Jan. 30, 1996, to Yamamoto et al. While blade tilt steering does provide an effective means for making course corrections, it presents other problems. Most notably, blade tilt steering can result in an uneven surface after dozing due to the various tilt angles that the blade occupies during a push.
This invention is directed to overcoming one or more of the above-described problems.